1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device of a thin film transistor (hereinafter referred to as xe2x80x9cTFTxe2x80x9d) type or the like and a manufacturing method thereof.
2. Description of the Related Art
A liquid crystal display device, in view of its characteristics that the device is thin, light-weighted and exhibits low power consumption, has been popularly used as a display equipment for image information and character information of an information equipment as represented by a personal computer, a portable information terminal, a portable telephone, a digital camera, and a visual equipment such as a camera-built-in type VTR equipment. Recently, along with spreading of large-capacity media or starting of BS digital broadcasting due to the advent of DVD and the rapid progress of large-capacity magnetic drives, the fusion of a personal computer and a video digital media is in progress and the demand for an image display device having high image quality which can cope with such an application is increased. A liquid crystal display adopting an in-plane switching (IPS) mode which applies a lateral electric field to liquid crystal sealed in a gap defined between upper and lower substrates has been recognized as a display method which is capable of satisfying such a demand for high image quality and various improvements have been made aiming at the further enhancement of the image quality.
On the other hand, along with spreading of portable telephones and portable information terminals, the demand for medium-sized or small-sized liquid crystal display devices which exhibit extremely small power consumption has been increased.
In the liquid crystal display device adopting the IPS mode, as disclosed in Japanese Patent Laid Open H07-36058, a method which performs switching of liquid crystal using a lateral electric field which is generated between two-layered metal electrodes sandwiching an insulation film therebetween has been most popularly used. A defect of such a structure lies in that, compared to a display device adopting a usual TN method, it is difficult to increase the numerical aperture of pixels so that the light utilization efficiency is low. Since it is necessary to increase the brightness of a backlight to compensate for this defect, as the whole LCD module, it is difficult to seek for the low power consumption which is demanded with respect to a notebook type personal computer or a portable terminal.
In the IPS type liquid crystal display device, there has been a task that the IPS type liquid crystal display device exhibits the smaller numerical aperture compared to the TN type liquid crystal display device and hence, it is necessary to enhance the numerical aperture. The IPS type liquid crystal display device also has a task that the brightness must be increased to cope with the video digital media. Further, the IPS type liquid crystal display device has a task that the low power consumption must be realized.
Further, inventors of the present application also have found a following new task. That is, when portions of the pixel electrodes or the common electrode are constituted of transparent conductors such as indium-tin-oxide (ITO), for example, light passes through a region of a fixed width from an end of the electrode and hence, the numerical aperture (transmissivity) can be substantially increased. However, when liquid crystal material is formed of positive-type material, liquid crystal molecules at an end portion have components which are erected with respect to a surface of a substrate due to applying of the electric field and are arranged obliquely with respect to the transmitting light and hence, a viewing angle becomes narrow and the wide viewing angle which is the characteristics of the IPS type liquid crystal display device is damaged.
Further, the present invention also copes with a task to suppress the increase of a leak current when the TFTs are turned off which is generated due to the increase of a light irradiation amount to semiconductor elements to cope with high brightness.
One of the advantages of the present invention is to improve or solve one or a plurality of these tasks. To describe some of advantages realize in any one of the present invention in detail, they are as follows. The first advantage is enable providing a liquid crystal display device which can arrange the holding capacitance in an increased quantity without deteriorating the numerical aperture (transmissivity) in an IPS type liquid crystal display device using low-temperature polysilicon TFTs as pixel TFTs. The second advantage is enable providing a liquid crystal display device which can enhance the numerical aperture (transmissivity) by dividing each pixel into four or more portions or increases the holding capacitance when the pixel electrodes or the common electrode are arranged on organic resin in an IPS type liquid crystal display device. The third advantage is enable providing a liquid crystal display device which can satisfy both of broad viewing angle characteristics and low voltage driving.
Other advantages and tasks of the present invention will be apparent in the specification of this application described hereinafter. To describe major examples of the present invention, they are as follows.
(1) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode line, a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, the common electrode is formed over the drain line by way of an insulation film and the pixel electrode has a comb-teeth shape and is formed over the same layer as the common electrode, at least one of comb-teeth shaped portions of the pixel electrode has a multi-layered structure, and a holding capacitance is formed by a pixel electrode which constitutes a lower layer out of the multi-layered pixel electrode and the common electrode line layer.
(2) In (1), the common electrode line is formed substantially parallel to the gate line, and the common electrode and the common electrode line are connected through apertured portions of an insulation film including the insulation film.
(3) In either one of (1) and (2), the pixel electrode which constitutes the lower layer is arranged on the other layer of the pixel electrode by way of an insulation film.
(4) In any one of (1) to (3), the liquid crystal display device includes at least four main light transmitting portions which are formed within one pixel along a transverse line extending between the neighboring drain lines, the pixel further includes a through hole portion through which the common electrode on the drain line and the common electrode line are connected therein, and the pixel electrode which is disposed close to the drain line arranged at a side remote from the through hole portion within the pixel forms the holding capacitance.
(5) In any one of (1) to (4), the TFT element is formed of polysilicon and an insulation film of the holding capacitance is formed of an inorganic insulation film which covers the gate line of the TFT element.
(6) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, the common electrode and the pixel electrode are formed over the same insulation film, and the pixel further includes a metal electrode which has a portion thereof superposed in a planar manner to a gap formed between the common electrode and the pixel electrode by way of an insulation film, and a potential equal to a potential applied to the common electrode or the pixel electrode is applied to the metal electrode.
(7) In (6), ends of patterns of the pixel electrodes and the common electrodes which are arranged on the insulation film are formed of a transparent electrode.
(8) In (6), the insulation film is formed of an organic insulation film made of acrylic resin or the like.
(9) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, a region of one pixel arranged between the neighboring drain lines includes at least four-divided apertured portions between the drain lines, and widths of the divided respective apertured portions are formed in the order of sum of widths of the electrodes disposed at both sides of each apertured portion.
(10) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, a common electrode line, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, the improvement is characterized in that a region of one pixel arranged between the neighboring drain lines includes at least four-divided apertured portions between the drain lines, the common electrode is formed over the drain line by way of an insulation film and the pixel electrode has a comb-teeth shape and is formed over the same layer as the common electrode, and at least one of the pixel electrodes has a multi-layered structure, and a holding capacitance is formed by a pixel electrode which constitutes a lower layer of the multi-layered pixel electrode and the common electrode line layer, and a width of the apertured portion between the pixel electrode which forms the holding capacitance and the common electrode on the drain line close to the pixel electrode is set wider than a width of other apertured portions.
(11) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, a region of one pixel sandwiched between the neighboring drain lines includes at least four-divided apertured portions between the drain lines, and widths of the four-divided respective apertured portions differ from each other.
(12) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, the common electrode is formed over the drain line by way of an insulation film and the pixel electrode is formed of a transparent conductive body being formed over the same layer as the common electrode and having a width narrower than a width of the common electrode, and ends of the pixel electrode in the widthwise direction are shielded from light by a metal electrode which is arranged below the insulation film and to which a potential equal to a potential applied to the pixel electrode is applied.
(13) In (12), the width of the metal electrode is set wider than the width of the pixel electrode formed of the transparent conductor.
(14) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, a region of one pixel arranged between the neighboring drain lines includes at least four-divided apertured portions between the drain lines, and widths of the apertured portions are set to at least two or more different values, and the width of the apertured portion having a large sum of the widths of the electrodes arranged at both sides of the apertured portion is made wider than the width of the apertured portion having a small sum of the widths of the electrodes arranged at both sides of the apertured portion.
(15) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, the common electrode is formed over the drain line by way of an insulation film, the pixel electrode is formed over the same layer as the common electrode and is formed of a transparent conductive body having a width narrower than a width of the common electrode, and ends of the pixel electrode in the length direction are shielded from light by a metal electrode which is arranged below the insulation film and to which a potential equal to a potential of the pixel electrode is applied.
To mention further examples of the present invention, they are as follows.
To realize the first advantage of this invention, some examples are as follows.
Pixel electrodes which constitute portions for forming a display electric field and extend with a narrow width and common electrode potential portions which are superposed on the pixel electrodes by way of an insulation film are provided, and a holding capacitance is formed between the pixel electrodes extending with a narrow width and the common electrode potential portions.
The common electrodes for forming a holding capacitance extend below the pixel electrode by way of one insulation film and extend above the pixel electrodes by way of the other insulation film whereby the holding capacitance can be increased.
The common electrodes which extend above the pixel electrodes by way of the other insulation film are formed of a transparent electrode and are projected to cover at least one end of the extending pixel electrode so that the increase of the holding capacitance can be increased without sacrificing the numerical aperture.
To realize the second advantage of this invention, some examples are as follows.
Pixel which includes a connection region which connects the common electrode formed over the drain line and the common electrode or a reference signal line formed as a layer below the drain line via the through hole and four or more apertured portions between comb-shaped teeth in one pixel region, wherein a holding capacitance is formed by the pixel electrode having a comb-teeth shape and arranged opposite to the connection region and the common electrode.
Another examples for achieving the second advantage of the present invention lies in that, in the IPS display device having pixels each of which has four or more main aperture regions, as potentials for driving the liquid crystal of the main light transmitting portions, a potential of the common electrode on the drain line, a potential of the non-covered common electrode on the drain line which is connected to the common electrode, and a potential of the pixel electrode which forms the same layer as the common electrode on the drain line are provided. The advantageous effect can be enhanced by forming at least one or both of the common electrode and the pixel electrode using a transparent electrode.
Another examples for achieving the second advantage of the present invention lies in that, in the IPS display device in which each pixel has four or more light transmission regions between neighboring drain lines, the widths of all light transmission regions differ from each other. Particularly, by arranging the widths of the transmission regions in the reverse order of the sum of widths of comb-teeth at both sides of the transmission region, the maximum effective transmissivity can be obtained. Further, as the width of the pixel electrode, by setting the comb-teeth width of a portion of the comb-teeth which forms the holding capacitance out of the comb-teeth to a large value, it is possible to increase the capacitance to the maximum. By setting the distance between the common electrode which is formed above the drain lines by way of the insulation film and the comb teeth of the pixel electrode which form the holding capacitance to a large value, the second object can be obtained to the maximum.
To realize the third advantage of this invention, some examples are as follows.
At least one of the pixel electrode or the common electrode arranged on the insulation film is formed of the transparent electrode, at least one end portion of the extending comb teeth has a portion which is superposed on the electrode arranged as a layer below the transparent electrode while sandwiching the insulation film therebetween, and the electrode is shielded from light by the light-shielding metal electrode to which a potential equal to a potential applied to the transparent electrode is applied.
Further examples of the present invention will be apparent in the embodiments of the present invention which are explained hereinafter.